border-1px($color)
  position relative
  &:after
    display block
    position absolute
    left 0
    bottom: 0
    width: 100%
    border-top: 1px solid $color
    counter: ' '
border-none()
  &:after
    display: none
// 处理图片
bg-image($url)
  background-image: url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image: url($url + "@3x.png")  